This invention relates to receivers operating in the microwave and millimeter wavebands which comprise a dielectric lens which focusses incoming radiation onto a detector array. In particular, but not exclusively, this invention relates to such receivers for surveillance and/or tracking systems, for example for missiles.
In such applications it is desireable to have a light and compact arrangement with a high relative aperture (typically f1.0) and a wide field of view.
In one system, the dielectric lens focusses incoming radiation onto an array of crossed dipoles (typically 8.times.8) or slots interconnected with each other and with an IF output circuit by means of diodes which, together with the components of the IF circuit may be formed monolithically in a substrate of material of the same dielectric constant as the lens material attached to the lens. The two dipoles of each pair respond respectively to the linearly polarised received radiation and to an orthogonally linearly polarised local oscillator signal which is radiated directly on to the array and these two signals are mixed to form an IF signal.
The local oscillator signal may be radiated onto the antenna/mixer array in the same direction as the incoming received radiation, for example by employing a patch antenna located on the front surface of the lens or by means of a polarising reflector located either forwardly of the lens or in the lens material itself and supplied with a local oscillator signal from a transversely directed source.
In order to achieve the collection and focussing of radiation several systems have been proposed; a lens in combination with one or more reflectors; a two lens arrangement, and a single large lens element. These systems can be large and heavy and the performance and field of view can be limited. These properties therefore militate against adoption of the receiver in environments where space and weight allowances are limited.